In a case of forming a ferroelectric thin film, which is used in a dielectric layer such as a thin film capacitor, by a sol-gel method, a manufacturing process is adopted in which a substrate is coated with a sol-gel liquid for forming the thin film, and the coating film is subjected to temporary firing and permanent firing. In this case, if the amount of the sol-gel liquid used for a single coating operation is increased so as to obtain a thicker film, the tensile stress occurring in the film at the time of permanent firing or the like increases, and this leads to a problem in that cracks are generated in the thin film after permanent firing.
If there are cracks in the formed thin film, the electrical characteristics and the like thereof deteriorate. Therefore, conventionally, in the sol-gel method, the thickness of the film that can be formed by a single coating operation is limited to about 100 nm. In order to form a thick ferroelectric thin film, coating, permanent firing, and the like of the composition are repeatedly performed plural times, and therefore, the manufacturing efficiency of the thin film is reduced, and the costs increase.
Therefore, conventionally, a raw material liquid that can form a thick coating film by a single coating operation has been examined. For example, Patent Document discloses that by adding propylene glycol to a raw material liquid forming a Ti-containing metal oxide thin film, it is possible to form a thin film which does not crack even if a thick film having a thickness of equal to or greater than 0.2 μm is formed by a single coating operation. Furthermore, Non-Patent Document 1 discloses that by adding a polymer compound to a high concentration sol-gel liquid for forming a ferroelectric thin film, the tensile stress occurring during the film formation is released, and therefore, it is possible to form a thin film without cracking the film even if the thickness of the coating film formed by a single coating operation is increased.
In addition, regarding a composition for forming a metal oxide thin film using a metal alkoxide, a method is known in which a hydrophilic polymer such as polyvinyl pyrrolidone (PVP) or polyvinyl acetamide (PNVA) is added to a solvent containing a chelate such as acetic acid, and the obtained composition is used to form a thin film having a thickness of equal to or greater than 0.5 μm by a single coating operation (Patent Documents 2 and 3).